changes to ping MIB conformance material

Hi -

Merging in another implementation report on the DISMAN-PING-MIB
module has left me wondering whether it was a good idea to remove
the pingCompliance and pingGroup OBJECT-GROUP.  I find that I
have to go back to RFC 2925 to make sense of implementation reports,
and that when someone says they implement the pingGroup, that
has no meaning in terms of the current i-d.  This doesn't seem right.
Comments?

Randy